It has already been suggested, e.g. in the U.S. Pat. No. 4,350,259 to manufacture a cooking pot made of stainless steel with a thermal conducting bottom of aluminum and/or of an alloy of this metal. Such a cooking pot is suitable for being heated by different sources of heat, regardless of whether this is by the gas heating devices, an electrical hot plate or by induction. The cooking pot which is produced is composed at least of one, preferably of two layers of aluminum or an alloy containing the metal and of a laminated steel or iron plate fixed in this aluminum layer or inserted between the two aluminum layers. Preferably the laminated bottom plate of steel is magnetized, so that it allows the cooking pot to be heated by induced currents. The laminated iron plate is provided with perforations which can be constituted by simple holes or openings presenting an undulating or zigzag contour, the perforations being intended to permit the aluminum to creep while the bottom is being manufactured. In this way, a direct metallic bond is obtained between the two layers of aluminum.
It must be taken into account that the cooking pots manufactured according to the above-mentioned technique give suitable results. On the other hand, this type of pot does not completely solve the well-known problem of thermal expansion and/or deformations occurring at the bottom. In the action of heat from the heating means lead all more easily to harmful expansions or deformations as the bottom contains several coats of different compound materials. In the longterm a deformation of the cooking pots can be noticed and especially a detachment of the thermal conducting layers or even cracks in the metal continuity between the aluminum layer or layers and the laminated steel plate. The thermal conductivity of the cooking pot is affected which leads in general to a reduced thermal output and to a longer cooking time. In the specific case of cooking pots with a magnetic bottom one will also notice partial cracking in the continuity of the induced currents generated in the steel plate which leads to poor heat transfer.